The present invention generally relates to liquid crystal display devices and more particularly to a liquid crystal display device of vertical alignment (VA) mode.
A liquid crystal display device is a display device having the feature of compact size and small electric power consumption. Thus, a liquid crystal display device has been used extensively for various portable information processing apparatuses, particularly laptop computers or cellular phones. On the other hand, much progress has been made with regard to the performance of liquid crystal display device in the past, including the response speed and contrast ratio, and a liquid crystal display device is used nowadays also for replacing conventional CRT display apparatuses of desktop computers and workstations.
Further, in recent years, there are increasing instances in which a liquid crystal display device is used for displaying images in a television set ranging from a large screen television set to a compact portable television set. In the case of using a liquid crystal display device for a television set, there is imposed a demand that the liquid crystal display device is capable of displaying a motion picture with high speed.
Meanwhile, a liquid crystal display device of the vertical alignment mode, particularly the liquid crystal display device of MVA mode is used extensively for the display devices of computers and cellular phones in view of its excellent contrast ratio and wide viewing angle characteristics. It should be noted that the liquid crystal display device of MVA mode or MVA liquid crystal display device is a liquid crystal display device in which there are formed plural domains of different tilting directions of liquid crystal molecules in a single pixel region.
Thus, there is a natural demand of using such a liquid display device of MVA mode also for the display of television images.
FIGS. 1A and 1B are diagrams showing the principle of a MVA liquid crystal device 10 proposed by the inventor of the present invention, wherein FIG. 1A shows the liquid crystal display device 10 in the non-activated state in which there is applied no driving electric field to a liquid crystal layer 12, while FIG. 1B shows the same liquid crystal display device 10 in an activated state in which a driving electric field is applied to the liquid crystal layer 12.
Referring to FIG. 1A, the liquid crystal layer 12 is held between a glass substrate 11A and a glass substrate 11B, wherein the glass substrate 11A and 11B form a liquid crystal panel together with the liquid crystal layer 12.
On each of the glass substrates 11A and 11B, there are formed respective alignment films not illustrated, wherein the alignment films control the pointing direction of the liquid crystal molecules of the liquid crystal layer 12 such that the liquid crystal molecules are aligned in a direction generally perpendicular to the liquid crystal layer 12 in the non-activated state in which no drive electric field is applied to the liquid crystal layer 12.
In this state, the optical beam incident to the liquid crystal display device undergoes no substantial rotation of its polarization plane as it passes through the liquid crystal layer, and thus, the optical beam incident to the liquid crystal layer 12 through a polarizer is interrupted by an analyzer, provided that the polarizer and the analyzer are disposed above and below the liquid crystal panel in a crossed Nicol relationship.
In the activated state of FIG. 1B, on the other hand, the liquid molecules are tilted as a result of the applied electric field, and because of this, the optical beam incident to the liquid crystal layer undergoes rotation of the polarization plane thereof. As a result, the optical beam incident to the liquid crystal layer 12 through the polarizer passes also through the analyzer.
Further, in the liquid crystal display device 10 of FIGS. 1A and 1B, there are formed projecting patterns 13A and 13B respectively on the glass substrates 11A and 11B so as to extend parallel with each other, wherein the projecting patterns 13A and 13B impose localized constraint with regard to the tilting direction of the liquid crystal molecules particularly at the time of transition from the non-activated state to the activated state. With this, the response speed of the liquid crystal display device 10 is improved.
By forming such projecting patterns 13A and 13B, not only the response speed of the liquid crystal display device 10 is improved, but there are also formed plural domains of different tilting directions of the liquid crystal molecules in the liquid crystal layer. Thereby, the viewing angle characteristics of the liquid crystal display device are improved significantly.
[Patent Reference 1] Japanese Laid-Open Patent Application 2002-107730 gazette
[Patent Reference 2] Japanese Laid-Open Patent Application 2002-357830 gazette